Sam Wallace: A match that can shape Arsenal's future – and Wenger's legacy

Tonight's result is key to keeping stars at the Emirates, and proving their manager's philosophy right

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Does a manager need to win the European Cup in order to be considered truly great? It is the kind of question that Arsène Wenger yesterday said might come to haunt him if his Arsenal team are eliminated by Manchester United in the Champions League semi-final second-leg tie tonight.

By way of balance, Wenger added that there were plenty of managers for whom winning the European Cup was just about the only thing they achieved in their careers. Like Tony Barton, someone said. And as if to illustrate his point perfectly Wenger replied, with a hint of embarrassment: "Who?"

The trouble for Wenger is that unlike Aston Villa's victorious manager in 1982, he has won so much that the absence of Europe's most coveted trophy, or indeed any European trophy, is stark. The brilliance of Wenger at Arsenal will live on regardless but when he says that winning the Champions League is an obsession he is only half-right. Rather the obsession for Wenger is that the Champions League must be won his way, with his young players, on his terms.

All of that makes tonight's game at the Emirates, with Arsenal chasing a 1-0 deficit from the first leg at Old Trafford, even more absorbing and yesterday Wenger was at his effusive best, theorising on some of the big questions, including his belief that managers are only truly appreciated after they die. He claimed that if he had announced in November that Arsenal would be in the Champions League semi-finals, "You would have called an ambulance". He even started singing a Beatles song at one point.

The song in question was "Yesterday" although yesterday, Wenger made plain, has no value for him. He claimed he has never watched a recording of Arsenal's 2006 Champions League final defeat to Barcelona. He said that he also gives away his football medals to friends because the past is meaningless to him. "Because for me what is important is what's happening tomorrow," Wenger said. "What is done is done."

There are reasons not to look back on a season that started with five defeats in Arsenal's first 14 Premier League games; a period during which Wenger steadfastly refused to acknowledge the shortcomings in his squad. Yet for all their subsequent progress nothing would be quite as extraordinary as Arsenal eliminating the defending champions tonight with a patched-up defence and a first-leg performance that looked, quite frankly, like they had run out of ideas.

As ever, for Wenger anything is possible with this young team of his. Bacary Sagna, Kieran Gibbs, Denilson, Alex Song and Abou Diaby are all his discoveries, plucked from virtual anonymity. Then there are the likes of Robin van Persie, Emmanuel Adebayor, Manuel Almunia, even Mikaël Silvestre: misfits that no big club was quite prepared to take a chance on. It is not enough for Wenger to win the Champions League, he has to win it with his team of foundlings and cut-price superstars.

Wenger talked of his pride at a team who had been "through difficult periods, shown great mental strength" and he returned to his favourite mantra. "You take the lists of players in the Champions League semi-finals and you calculate the average age of each team and you will see that we are four to five years younger than any other team." That really matters to Wenger although he may be the only one in Arsenal colours for whom it is a consolation if things go awry tonight.

As he ignores yesterday and concentrates on tomorrow, the next major battle for Wenger, beyond Sir Alex Ferguson tonight, will be keeping hold of the team that he has built, significantly players such as Cesc Fabregas and Adebayor. "They all have contracts and we have educated them to stay together for years – we will fight very hard for that," he said. Fabregas said again yesterday that he was at Arsenal for the long haul but Wenger had a more persuasive reason. "For 90 per cent of the players it is the club that makes their career," he said. "There are good players in small clubs. Look at the squads of the teams struggling to stay up and they have some players who are very good. If you are at one of the ten biggest clubs at 21, 22 and you have been educated and you get your chance why should you want to move?"

As for Adebayor, he acknowledged fans' frustration but defended the striker against criticism of his performance in the first leg. "I watched that game carefully and he put a lot more effort in, more than people think, and he was really isolated. We didn't give him enough support. He's focused and he wants to do well."

On his team, Wenger is unequivocal: he has backed them through the lowest points and to an extent they have rewarded him by coming this far. On himself, and his own attitude towards success, the Arsenal manager is more evasive. His claim that he has never watched a recording of the 2006 final against Barcelona contradicted what he said last month. On his own legacy, he hinted at the frustrations he feels at how his approach to the job is interpreted.

What Wenger said is that when it came to being the "greatest manager in history", as he put it, he did not know or care exactly how that would be accomplished. "Once I'm not there anymore what can I do about that? Usually you need to die to be great." Later on he said that he was only worried about doing his best for the club. "Other people can judge [me] immediately after. You need distance."

The time for reflection will come if Arsenal are eliminated tonight, a prospect Wenger refuses to contemplate. For weeks he has been saying the same about the title, refusing to acknowledge that Arsenal winning it is implausible until it became mathematically impossible. United's victory over Middlesbrough on Saturday made it just that for Arsenal although with Wenger in such a sunny mood yesterday it felt rude to point it out. His team, he said, are still the "super-outsiders" tonight but Wenger's belief in them is unwavering.

Four to go?: Gunners who could move on if European glory proves elusive

Theo Walcott: Has developed into one of Arsenal's key players but has yet to sign an extension to his contract, which runs to 2010. Enjoying his best season to date – 31 games, nine goals – the 20-year-old winger would attract huge interest were he to look for a move.

Cesc Fabregas: Arsène Wenger's most loyal disciple constantly reaffirms his commitment to the Arsenal cause but has also touched on his impatience to win silverware. Real Madrid and Barcelona, the club the Gunners took the 22-year-old from, will watch developments with interest.

Emmanuel Adebayor: Talk of a move to Milan persisted throughout last summer, rumours that the striker did little to dampen thus earning the ire of the Arsenal fans. Another trophyless season will only see the transfer chat about the 25-year-old forward resurface.

Robin van Persie: Could leave on a free in summer of 2010 as his contract expires. Has been stalling on signing an extension, claiming he will look at things in the summer. The 25-year-old forward has been at Arsenal since 2004 with just an FA Cup winner's medal to show for it.